Filter candle

ABSTRACT

A filter candle for a precoated filter for filtering and/or stabilizing fluids, especially beer, the filter candle comprising a tubular filter body that is formed from a spirally wound wire, with gaps being provided between the wire windings as fluid passages. To improve the adhesion of the precoated filter in such a filter candle, the surface of the wound wire that rests against the exterior of the filter body is inclined by an angle α relative to the longitudinal axis of the filter candle.

FIELD OF THE INVENTION

The present invention relates to a filter candle for a precoated filterfor filtering and/or stabilizing fluids, especially beer, the filtercandle comprising a tubular filter body formed from a spirally woundwire, with gaps being provided between the wire windings as fluidpassages.

BACKGROUND OF THE INVENTION

Precoated filters are especially needed in beer brewing to filter outthe turbid matter contained in the beer and/or to stabilize the beer. Ina known precoated filter, filter candles are used, in which the filterbody comprises a wound wire, with gaps between the wire windings servingas fluid passages. The wound wire is either self-supported, or it isheld by a carrier communicating with the wound wire. The filter candlesof the precoated filter are arranged in an unfiltrate chamber, thenpassing the filtrate onwards into a filtrate area. For filtration,filtering aids, such as kieselguhr (diatomaceous earth), cellulose,pearlite, activated carbon, plastic fibers, glass fibers, cellulosefibers, or the like, are added to the beer to be filtered. Duringfiltration the filtering aids are precoated on the exterior of thefilter body at the beginning of the filtering operation, resulting inthe formation of a precoat layer which, in turn, serves as a filteringlayer.

The adhesion of the precoat layer to the filter body surface is of greatimportance, especially to process reliability, because a slipping offmay lead to a destruction of the filter cake structure and thus also toan inadequate filter quality. The known filter bodies of wound wire,however, do not always yield an optimum adhesion of the filtering aid tothe filter body, so that there may be malfunctions.

SUMMARY OF THE INVENTION

It is therefore the object of the present invention to provide a filtercandle for filtering fluids, the filter candle permitting improvedadhesion of the precoat layer.

According to the invention said object is achieved in that the surfaceof the wound wire that rests against the exterior of the filter body isinclined by an angle α relative to the longitudinal axis L of the filtercandle.

Due to the inclination of the surface of the wound wire that restsagainst the exterior of the filter body, there is an offset of thesurfaces of successive windings, so that the precoat layer can adhere inan improved manner. Despite said improved adhesion, there is also animproved back-washing possibility of the precoat layer because the riskof blocking is smaller thanks to the inventive arrangement of the woundwire.

The same advantages are also achieved during the separate orsimultaneous stabilization of beer with stabilizing agents, such aspolyvinylpolypyrrolidone (PVPP) or filtering aids, such as silica gels,because the adhesive power thereof is particularly critical.

The angle α is preferably within a range between 1° and 10°, preferablybetween 3° and 5°. In this range the inclined winding of the wire can berealized in a simple way, entailing a distinct improvement of theadhesion of the precoat layer.

Preferably, the wire has a substantially triangular, inwardly taperingcross-section, so that the baseline of the triangle rests on theexterior of the filter body. This yields a gap width that increases fromthe exterior of the filter body to the interior.

Advantageously, the upper edge and the lower edge of the inclinedsurface of the wound wire are rounded, which may already be due tomanufacture. The rounded edges can reduce the risk of blocking evenfurther during back-washing of the filter.

In a filter candle developed according to the invention, the lower edgeof the inclined surface of a first winding relative to an upper edge ofthe inclined surface of a wire winding positioned thereunder is offsetinwards, the radial offset thereinbetween being in the order of tenthsof a mm. Preferably, all lower edges of the inclined surfaces arepositioned along a straight line parallel to the longitudinal axis L ofthe filter body, and all upper edges of the inclined surface along asecond straight line parallel to the longitudinal axis L of the filterbody. This arrangement makes it possible that the precoat material, suchas kieselguhr, can easily deposit between the mutually offset lower andupper edges of the successive inclined surfaces.

The present invention also relates to a precoated filter which comprisesa filter vessel with an unfiltrate chamber, with filter candles beingarranged in the unfiltrate chamber for filtering fluids.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention shall now be explained with reference to the followingfigures in more detail, in which:

FIG. 1 schematically shows a longitudinal section through an embodimentof the filter candle according to the invention;

FIG. 1A shows a section along line A—A of FIG. 1;

FIG. 2 shows an enlarged section Z of FIG. 1;

FIG. 3 shows an enlarged section Y of FIG. 2; and

FIG. 4 is a schematic section through a precoated filter comprising thefilter candles according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

As becomes apparent from FIG. 4, the filter candles according to theinvention for filtering fluids, particularly beer, can be suspended inan unfiltrate chamber 15 of a filter vessel 13. In this instance, thefilter candles are secured to a partition wall 12 which subdivides thefilter vessel 13 into a filtrate chamber 14 and the unfiltrate chamber15. The fluid to be filtered, such as beer, to which kieselguhr has beenadded as a filtering aid, is introduced via the inlet 30 into theunfiltrate chamber of the filter vessel 13. From said place it passesthrough the precoat layer, which has formed before and during filtrationby kieselguhr depositing on the exterior surface of the filter candles,and then passes through the fluid inlets 12 (FIG. 2), which are formedby gaps between the wire windings 17, into the interior of the filtercandle and is finally passed into the filtrate chamber 14 from where itthen exists via an outlet 16 out of the filter vessel.

As becomes apparent from FIG. 1, the filter candle 1 in this embodimentcomprises a filter body 2 which is formed from a spirally wound wire 17.The filter body is connected via spacers 4 to an inner body, here aninner tube 3, which serves to reduce the volume of the interior of thefilter body 2. The wound wire 17 is thus held and supported by the innertube with the spacers 4. The inner tube 3, the spacers 4 and the woundwire 17 form filtrate channels 6 (FIG. 1 a) through which the filtratecan flow through the filter candle upwards to the recesses 9 and fromthere via the head portion 7 into the filtrate area 14. The filter body2 is closed by a head portion 7 and an end portion 5. The invention,however, is not limited to said embodiment; of course, the wire woundaccording to the invention may also be self-supporting, e.g. due towelded support wires in axial direction, or it may comprise a differentcarrier construction.

FIG. 2 shows, on an enlarged scale, area Z of FIG. 1. As follows fromsaid FIG. 2, the spirally wound wire 17, which is here welded to thespacer element 4, which extends in the form of a rod in the longitudinaldirection of the filter body 2, has a substantially triangularcross-sectional shape. The baseline g of the acute triangle ispositioned on the exterior of the filter body 2. The baseline g haspreferably a length between 0.5 to 3 mm. Height h of the acute triangleis from 1 to 5 mm. The surface 20 of the wound wire 17, which forms theexterior of the filter body 2 (baseline g), is inclined at an angle αrelative to the longitudinal axis L of the filter candle. In thisembodiment, said angle α is about 3°. The inclined surface 20 may eitherbe achieved by an inclined winding of the wire 17 or by choosing thecross-section of the wire 17 such that the cross-section of the triangleis not an acute isosceles triangle, but an acute non-isosceles triangle,resulting also in the inclined position of the surface. The lower edge21 of the inclined surface 20 of a first wire winding is offset inwardsrelative to the upper edge 22 of the inclined surface 20 of a wirewinding positioned thereunder. The offset r (FIG. 3) is identical withthe distance between a first plane imagined along the inclined surface20 of a first winding, to a second plane extending along the inclinedsurface 20 of a successive winding. The radial offset r is between about0.5 to about 2 mm. Thanks to the offset of the lower edge 21 relative tothe upper edge 22, the upper edge 22 projects to the outside relative tothe lower edge positioned thereabove, so that filtering aids can herevery easily deposit as a precoat layer and can get fixed and securedagainst slipping downwards. All of the lower edges 21 of the inclinedsurface 20 are positioned along a straight line parallel to thelongitudinal axis L of the filter body, and all of the upper edges 22 ofthe inclined surfaces 20 are along a second straight line parallel tothe longitudinal axis L. Hence, the filter body 2 has a constantdiameter over its whole length L.

As follows from FIG. 3, the lower edge 21 and the upper edge 2 arerounded. This is of advantage because the risk of blocking is therebyreduced further.

The fluid passages are formed by the gaps 11 between the respective wirewindings. The gap width between the lower edge 21 of a first wirewinding and the surface 23 of the wire of the neighboring winding b1facing the lower edge 21 is preferably between 5–8/100 mm when a beerfilter is used, the perpendicular of the base g of a winding to theupper surface 23 of the neighboring winding being regarded as distanceb1, as follows from FIG. 3. The gap width increases towards the interiorof the filter body 2 due to the triangular cross-section of the wire.

In the illustrated embodiment, the upper edge of the wound wire ispositioned relative to the filter body axis further to the outside thanthe lower edge of the wire. The present invention, however, should notbe limited thereto because it is also possible, though not explicitlyshown, that the lower edge of the wound wire is positioned further tothe outside relative to the longitudinal axis L of the filter body 2 incomparison with the upper edge, i.e. the inclination is opposite to theinclination shown in the figures. In this instance, too, the irregularsurface permits an improved deposition of the precoat layer, resulting,in addition, in a simplified back-washing.

1. A filter candle (1) for a precoated filter for filtering and/orstabilizing fluids, comprising: a tubular filter body (2) formed from aspirally wound wire (17) and having gaps provided between the wirewindings as fluid passages, the surface (20) of the wound wire (17) thatis the exterior of the filter body (2) being inclined by an angle αrelative to the longitudinal axis (L) of the filter candle (1), and thewire (17) having a substantially triangular, inwardly taperingcross-section, with the baseline (f) of the triangle being the exteriorof the filter body (2), thereby resulting in an offset of the surface(20) of successive wire windings.
 2. The filter candle according toclaim 1, wherein the angle α is within a range between 1° and 10°. 3.The filter candle according to claim 2, wherein the angle α is within arange of between 3° and 5°.
 4. The filter candle according to claim 1,wherein the upper edge (22) and the lower edge (21) of the inclinedsurface (20) of the wound wire (17) are rounded.
 5. The filter candleaccording to claim 1, wherein the radial offset (r) between an upperedge of the inclined surface of a first wire winding and the lower edge(21) of the inclined surface of a subsequent wire winding is between1/10 mm and 1 mm.
 6. The filter candle according to claim 1, wherein thewire consists of a corrosion-resistant, food-compatible material.
 7. Aprecoated filter for filtering and/or stabilizing fluids, comprising: afilter vessel (13) including an unfiltrate chamber (15) in which filtercandles are arranged for filtering fluids, each filter candle having atubular filter body (2) formed from a spirally wound wire (17), andhaving gaps (11) provided between the wire windings as fluid passages,the surface (20) of the wound wire (17) that is the exterior of thefilter body (2) being inclined by an angle α relative to thelongitudinal axis (L) of the filter candle (1), and the wire (17) havinga substantially triangular, inwardly-tapering cross-section, with thebaseline (f) of the triangle being the exterior of the filter body (2),thereby resulting in an offset of the surfaces (20) of successive wirewindings.